U releases preliminary results of I-35W bridge study

An independent academic study conducted by the University of Minnesota found that poorly designed gusset plates were the cause of the Interstate 35W bridge collapse. Investment in the nationâÄôs infrastructure and the preliminary results of the UniversityâÄôs academic study of the bridge collapse were the focus of an Institute of Technology public lecture Wednesday night. These preliminary results were released almost a week after the National Transportation Safety Board presented parallel findings. The study, which began almost immediately after the collapse, used existing information and other tools to analyze the cause of the bridge collapse. Roberto Ballarini, University civil engineering professor and department head, said additional weight on the bridge the day it collapsed may have been a trigger to the accident, but the gusset plates were already unstable due to bad design. Temperature changes on the day of the collapse may have also caused additional stresses to the gusset plates. Ballarini used a paper clip to demonstrate the idea of elasticity. Generally, he said, when weight is put on a structure, the steel is supposed to bounce back. Safety measures should give the structure elasticity. However, in the case of the Interstate 35W bridge, the gusset plates were only a half inch thick, when they should have been one inch thick. The extra half inch would have provided the elasticity the bridge would have needed to bounce back. Instead, over time the pressure increased and the gusset plates, unable to bounce back, gave way, causing the collapse, he said. Ballarini completed this study along with several other professors and students in the civil engineering department. Their study was an academic exercise for the benefit of students. Minmao Liao, a graduate student in the civil engineering department, will use this study to write his masterâÄôs thesis. Ballarini used computer simulations to demonstrate high stress patterns in the gusset plates over time. Steve Crouch , dean of the Institute of technology, said Ballarini is a talented researcher, and he appointed him as head of the civil engineering department in 2007. According to the American Society of Civil Engineers , the United States received a D+ in road infrastructure, and a C in bridge infrastructure. âÄúThe problem is, when you live in an environment that is degraded, you might get used to it,âÄù Ballarini said. âÄúWe need innovation in our infrastructure, and we have to act soon.âÄù These findings are only preliminary. With new information being released, including that of the NTSB investigation, the University has more information to continue its research, Ballarini said. âÄúWe did our own investigation with what we had,âÄù Ballarini said. âÄúBut now we want to see if we can find out more and determine what ultimately made the bridge collapse that day.âÄù The researchers plan on publishing the final results in an academic research paper within the next six months. The study was funded by a grant from National Science Foundation , the UniversityâÄôs Center for Transportation Studies and the Civil Engineering Department.